ROS2 control, simple tutorial base on one continues joint

#ros2   #ros2_control  

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Table of Content

Objective

• Create simple urdf with two links and one continues joint
• Define controllers
  • Position
  • Velocity
  • Effort

robot.urdf

<?xml version="1.0"?>
<robot name="simple_example">
    <link name="world"/>

    <material name="blue">
        <color rgba="0 0 0.8 1"/>
    </material>

    <material name="black">
        <color rgba="0 0 0 1"/>
    </material>

    <joint name="word2base" type="fixed">
        <parent link="world"/>
        <child link="base_link"/>
    </joint>
    <link name="base_link">
        <inertial>
            <mass value="10" />
            <inertia ixx="0.4" ixy="0.0" ixz="0.0" iyy="0.4" iyz="0.0" izz="0.2"/>
        </inertial>
        <collision>
            <geometry>
                <cylinder radius="0.05" length="0.24" />
            </geometry>
        </collision>
        <visual>
            <geometry>
                <cylinder radius="0.05" length="0.24" />
            </geometry>
            <material name="black"/>
        </visual>
    </link>

    <link name="second_link">
        <inertial>
            <mass value="0.18" />
            <inertia ixx="0.0002835" ixy="0.0" ixz="0.0" iyy="0.0002835" iyz="0.0" izz="0.000324" />
        </inertial>
        <origin rpy="0.0 0.0 0.0" xyz="0.0 0.0 0.0" />
        <collision>
            <geometry>
                <box size="0.05 0.05 0.15" />
            </geometry>
        </collision>
        <visual>
            <geometry>
                <box size="0.05 0.05 0.15" />
            </geometry>
            <material name="blue"/>
        </visual>
    </link>

    <joint name="base_to_second_joint" type="continuous">
        <parent link="base_link"/>
        <child link="second_link"/>
        <axis xyz="0 0 1"/>
        <origin xyz="0.0 0.0 0.2" rpy="0.0 0.0 0.0"/>
    </joint>
</robot>

Position controller

• Add ros2_control definition to urdf
• Add gazebo plugin definition to urdf
• Add gazebo plugin yaml file
• Load controller
• Pub command

ros2_control

<ros2_control name="GazeboSystem" type="system">
    <hardware>
        <plugin>gazebo_ros2_control/GazeboSystem</plugin>
    </hardware>    
    <joint name="base_to_second_joint">
        <command_interface name="position"/>
        <state_interface name="position"/>
        <state_interface name="velocity"/>
        <state_interface name="effort"/>
    </joint>
</ros2_control>

ros2_Control plugin

<gazebo>
<plugin filename="libgazebo_ros2_control.so" name="gazebo_ros2_control">
    <parameters>$(find simple_joint)/config/position.yaml</parameters>
</plugin>
</gazebo>

position.yaml

controller_manager:
  ros__parameters:
    update_rate: 100  # Hz

    position_controller:
      type: position_controllers/JointGroupPositionController

    joint_state_broadcaster:
      type: joint_state_broadcaster/JointStateBroadcaster

position_controller:
  ros__parameters:
    joints:
      - base_to_second_joint
    interface_name: position
    command_interfaces:
      - position
    state_interfaces:
      - position
      - velocity

usage

```bash load controllers

joint_state

ros2 run controller_manager spawner joint_state_broadcaster

position controller

ros2 run controller_manager spawner position_controller

topics

ros2 topic list

/clock /joint_states /parameter_events /performance_metrics /position_controller/commands /position_controller/transition_event /robot_description /rosout /tf /tf_static

```bash title="pub position command
ros2 topic pub /position_controller/commands  std_msgs/msg/Float64MultiArray "{data: [340]}"